1. Field of the Invention
The present invention relates to a rotating electrical machine of permanent magnet implanted-type used for hybrid cars and the like.
2. Description of the Prior Art
Recent years, remarkable research and development of permanent magnets have driven development of permanent magnets each with high magnetic energy product, and to accordingly construction of rotating electrical machines each with higher power in a smaller size. In particular, with regard to rotating electrical machines for cars, such as for hybrid cars, large torque and high power are required to be produced in a limited space. In order to meet this requirement, rotating electrical machines need to be operated at high speeds by increasing forces of the respective permanent magnets.
In this case, large problems are strength of each rotor core against a higher centrifugal force, and a cooling required in response of increase in loss density. In addition, an eddy current to be generated in the surface of each of the permanent magnets is increased in response to the high-speed operation, and accordingly heat is generated. This causes heat demagnetization (irreversible demagnetization), and thus significantly reduces performances of the rotating electrical machine, such as power and efficiency. For this reason, this raises a serious problem.
With these taken into consideration, permanent magnet positioning protrusions 103 are provided to a rotating electrical machine of conventional type in a way that, for example, as shown in FIG. 1, each of the permanent magnet positioning protrusions 103 juts out into a corresponding permanent magnet implanting cavity 102 in a rotor core 101. Permanent magnets 104 are supported respectively with the permanent magnet positioning protrusions 103. Thereby, strength of each of thin portions on which stresses concentrate is secured. Thus, the rotating electrical machine of conventional type is intended to produce a high power, and to operate at a high speed. (Japanese Patent Laid-open Official Gazette No. 2001-339919).
In addition, the following method has been proposed as a method of cooling a rotating electrical machine using permanent magnets in a strengthened manner. As shown in FIG. 2, for example, a cooling air is caused to flow to the center portion of the shaft from each end part in the axial direction by use of permanent magnet implanting cavities 202 formed in a rotor core 201. Thereby, the center portion of the shaft and the permanent magnets are cooled down. A heating value is the largest in the center portion of the shaft. (Japanese Patent Laid-open Official Gazette No. 2004-343915, for example).
In the case of the rotating electrical machine disclosed by Japanese Patent Laid-open Official Gazette No. 2001-339919, the permanent magnets are supported with the protrusions, and thereby the strength of the rotor core is secured. This enables the rotating electrical machine to produce a high power at a high speed. However, in response to the high speed, iron loss and harmonic loss increase, and thus the temperature of the rotating electrical machine rises. In addition, heat of each of the permanent magnets stemming from eddy currents can not be sufficiently cooled down. As a result, the rotating electrical machine has a problem that the power and efficiency are reduced due to the temperature rise of the rotating electrical machine, and that the reliability is accordingly decreased.
Moreover, in the case of the rotating electrical machine according to Japanese Patent Laid-open Official Gazette No. 2004-343915, the strength of the rotor core against the centrifugal force can not be secured. This raises a problem that it is difficult for the rotating electrical machine to be operated at a high speed.